RUN_ONCE(9) | Kernel Developer's Manual | RUN_ONCE(9)

# NAME

RUN_ONCE — Run a function exactly once

# SYNOPSIS

#include <sys/once.h>

ONCE_DECL(control);

int
RUN_ONCE(once_t *control, int (*init_func)(void));

# DESCRIPTION

RUN_ONCE() provides a functionality similar to pthread_once(3). It ensures that, for a given control, init_func() is executed (successfully) exactly once. It is considered as a successful execution if and only if init_func() returned 0. As long as there was no successful execution, RUN_ONCE() will try again each time it is called.

RUN_ONCE() can sleep if it's called concurrently.

# RETURN VALUES

On failure, RUN_ONCE() returns what init_func() returned. Otherwise, it returns 0.

# EXAMPLES

The following example shows how RUN_ONCE() is used. Regardless of how many times some_func() is executed, init_func() will be executed exactly once.

    static int
    init_func(void)
    {

    	/*
    	 * do some initialization.
    	 */

    	return 0; /* success */
    }

    int
    some_func(void)
    {
    	static ONCE_DECL(control);

    	RUN_ONCE(&control, init_func);

    	/*
    	 * we are sure that init_func has already been completed here.
    	 */
    }

# SEE ALSO

pthread_once(3), condvar(9), intro(9)

July 7, 2010 | NetBSD 7.2